Epidemiologic features of HTLV-II: serologic and molecular evidence

A literature review was performed of the three principal subpopulations most commonly associated with human T-cell lymphotropic virus type II (HTLV-II) with the view of identifying the prevalence and transmission routes of HTLV-II. These included blood donors (BDs), intravenous drug users (IVDUs), and Amerindians (Indian populations from the Americas). We used the major criterion of serological and molecular distinction between human T-cell lymphotropic virus types I (HTLV-I) and II (HTLV-II). Three questions were formulated in addressing the possibility that HTLV-II might be responsible for the reported prevalence and transmission of this virus in these groups. Question One: Which population groups have the highest HTLV-II seroprevalence rates? Question Two: Are worldwide HTLV infection rates among the three sub-populations associated predominantly with the HTLV-II retrovirus type? Question three: What are the principal modes of transmission of HTLV-II?

Since earlier epidemiologic studies did not routinely use assays capable of distinguishing between HTLV-I and HTLV-II antibodies, their findings are necessarily inaccurate. However, with the more recent development of enhanced serologic assays, using recombinant antigens that are capable of accurately making this differentiation, it is now possible to more precisely define the epidemiology of HTLV-II. We reviewed only those studies where serological and molecular methods of accurately distinguishing between the two retroviruses were utilized. Initially, we located 36 studies, which met this particular review criterion. Of the five different assays we identified, the most prevalent were the polymerase chain reaction (PCR) (n = 14) and the synthetic peptide-based enzyme-linked immunoassay (Synth EIA) (n = 13). Our BD, IVDU, and Amerindian groups were also evaluated according to this differentiation schema. We were able to locate over 100 prevalence studies where focus was on some aspect of analysis of at least one or more of these three groups. By using many search terms - such as HTLV-II endemic population, seroepidemiological, as well as case control and cohort studies - we were able to create a comprehensive bibliographic database.

The two groups identified with high HTLV-II prevalence rates are the IVDUs and Amerindian population. The importance of breast-feeding, IVDU, and contaminated blood products in the HTLV-II transmission process is confirmed. Sexual intercourse, however, as a mode of HTLV-II transmission remains problematic.

By confining our evaluation to only those studies that used serological and/or molecular methods capable of distinguishing between the two retroviruses, we have been able to establish with confidence that there are consistent emerging patterns of HTLV-II infection in these populations.